Water treatment devices which treat water by discharge or electrolysis are known in the art. For example, Patent Document 1 discloses a water treatment device which purifies water by discharge.
A water treatment device includes a water tank, an interior space of which is divided into two treatment vessels by an insulating divider, and electrodes immersed one each in each of the treatment vessels. The divider is provided with a fine hole (discharge hole) which allows the two treatment vessels to communicate with each other. If a high voltage is applied from a power supply to the electrodes, current density at the fine hole increases as shown in FIG. 5 of Patent Document 1, and water in the fine hole is vaporized by Joule heat. As a result, a bubble is generated in the fine hole to divide the two treatment vessels from each other. In this water treatment device, an interface between water in one of the treatment vessels and the bubble and an interface between water in the other treatment vessel and the bubble function as electrodes. Then, discharge occurs from one of the interfaces of water to the other. The discharge thus occurred produces highly reactive materials (active species), such as hydroxyl radicals and hydrogen peroxide. Such active species purify or sterilize water.